are composed of two pieces (a few are more) of brass soldered together. It should go all the way closed, or the rod is bent or the spring is maladjusted. sidewall. If the RPM smooths out, then you found the problem. Too much air, or too much fuel? Top of the carburetor to the float bowl gasket may be leaking due to bad, or wrong gasket, or a warped float bowl, which is not uncommon on the Quadrajet. threads and crack the casting. The accelerator pump will squirt an extra bit of gas into the intake. Not all carburetors do. Once the liquid has been removed, and the leak has been marked, This can be caused by several things, but there is one item often missed by the rebuilder and that is the idle tube. Make sure they are in good condition and that the wires are properly connected. There My carb. Rochester was probably the most creative, often measuring to a dimple on the When the engine is started, the throttle should be tapped just a little to allow the choke to snap shut. This clearance If there is a 2nd line going to the gas tank, that is a vent. The following procedure works for Check your motors manual for correct pressure, probably around 4.5 lbs3. has more drag in the air; a brake disc or drum which is dragging or a front Determine whether carburetor is spewing or vapor locking. is less than 12 inches Hg. can also cause bog; as can a defective accelerator pump. other parts may be obtained through The Carburetor Shop LLC. First, check the two plugs in the bottom of the float bowl. Occasionally, the carburetor's idle jet will become clogged with dirt, which will cause the hesitation or stall. possible. It should get sucked up through the vacuum passage. dirt-daubers, (C) a fuel line fitting may have cracked, allowing air to enter Adjust to specification on vehicle emission control label +_ 2 1/2 deg for best engine operation. This is due to the low boiling point of the gas these days. Spark plug wires are an often-overlooked culprit. 12 page 14 of the Quadrojet models 4mv,4mc carburetor manual all are connected to the air horn. rochester 4mv quadrajet carburetor 1966 oldsmobile $ 455. 4) Adjust the mixture screws until the engine runs smoothly at all RPM ranges without hesitating or stalling. If the throttle valves were removed they may have been re installed incorrectly leaving too much air between the valves and the carb wall. This prevents the float bowl from filling quickly and results in poor engine performance. Nitrophyl floats have to be weighed. Many mechanics have been conditioned to ask for a float each time they timing, SET THE DWELL FIRST! an instantaneous bog, hesitation, or stumble upon acceleration. My carb. Next, remove the check ball screw and, when it is out, turn the body upside-down and the bearing ball will fall out. divorced choke resides on the manifold (divorced or remote from the carburetor) If not, the servo must be replaced because it operates with a rubber bladder inside and is leaking. Next, Adjust the throttle linkage. (9) an incorrect thickness carburetor to manifold gasket when the carburetor is With the engine idling, look down into the carburetor with a flashlight. Can't find the answer you're looking for? If the idle RPM is too high then the idle mixture isnt going to respond. This also may be a solution for a retired machinist with the tape, and ALLOW THE FLOAT TO COOL COMPLETELY before closing the Make sure the fuel lines are away from the exhaust.10. Most carb problems are attributed to dirt. It needs to move up and down freely. inverted flare seat (our favorite, but unfortunately, the manufacturer is now Also, are the secondary throttles opening and closing completely? the volatility). You should be getting 2 strong squirts of fuel from the venturi. Remove the short piece of vacuum hose attaching the choke pulloff to the vacuum nipple on the carb. Since it sits at the bottom of the float bowl, fuel has a tendency to drain back through the fuel system to the fuel tank. A Quadrajet is a unique carburetor in that it has small primary plates and huge secondary plates. 6.5-7.5 grams would be great. This can be done by performing the following road tests in 70 to 80 degree weather. Fuel delivery system test (less than 1 percent). Not all 4 jets will have this check ball. rebuild a carburetor, due to the reasonable price of modern, mass-produced This can be caused by one of several things, including electrical system problems. If you are a carburetion specialist, you already Make sure the power piston moves up and down freely. This specifications. Observe the pump jet in the carburetor, and For all you die-hards (or hardheads) there gasoline cap. These screws are usually located near the base of the carburetor, on either side. Remove the air cleaner. For all drivability complaints, check all vacuum hoses to make sure they are properly connected. HOW the manufacturer measured the adjustment. My first instinct is that he has a vacuum leak . The pressure will force Now test to see if the check ball seals by holding your finger over the main discharge hole and pressing down on the pump again. Weve got the answersthe Summit Racing tech department tackles your automotive-related conundrums. section is not designed to turn a novice into a professional mechanic, rather a solid gasket on a carburetor designed for the slotted gasket WILL result in As the valve opens there is less vacuum and the normal circuits take over. Possible items to fail - (A) the sock a.k.a. types of bog: the first is bog when the vehicle is accelerated from a stop; the The bushings are replaced only if you have excessive free play in the throttle shaft. Disconnect the throttle and try again in order to eliminate the linkage. OK, you rebuilt the carbs using correct parts to stock specs and now you are This could be caused by the needle to float clip being installed incorrectly. clearance between the center of the throttle plate edge, and the throttle body The inline, high-performance glass fuel filter displayed no. energy and will thus deliver worse fuel economy. (sometimes it helps to dampen the paper towel a bit). dirt-daubers, (C) a fuel line fitting may have cracked, allowing air to enter NOW YOU HAVE A BASELINE IF MODIFICATIONS ARE NECESSARY! Some Quadrajet carburetors have three. It was used on vehicles with air conditioning. Discussing these components: Q: I have seen numerous Rochester Quadrajet carburetors that have a leak down problem when the car sits idle for a day or more. The He has owned an auto service facility since 1982 and has over 45 years of technical experience as a master ASE tech. Finally, check to ensure that the vacuum lines which connect to the carburetor are hooked up correctly. The carb seems to be adjusted properly and the timing is correct for the engine. If so, then the check may be leaking. detonate in your engine (the higher grades often have more ethanol), (3) a replacement cork (or foam) float, and seal the cork (or foam) against the Replace any fuel filters - There is usually one in the fuel inlet of the carburetor and often there will be an in-line fuel filter. gaskets. The throttle linkage is located above the carburetor and below the main jet adjustment screws. Simply, there is too much gas getting into the float bowl. Mailbag Troubleshooting Rochester Quadrajet Carburetors. The car runs and starts right up. It is a good carburetor for up to close to 400 horsepower. inside the float, and a leaky float will blow a stream of bubbles. Needle is sticking in the seat. A 4 would mean it is for a Buick, a 5 would mean Oldsmobile, and Pontiac carburetors usually have a 6 or 7. Any chance you replaced the pump with a new one? (3) Only Runs With Choke Valve Partially Closed, So your engine seems to crap out once the engine gets warmed up.A vacuum leak can cause this. A gauge with a 0- 10 or 0-20 PSI should work. MUCH more efficiently. Bog from a stop is If the engine either hesitates or stalls upon acceleration due to the carburetor, the carburetor's accelerator pump nozzle may need to be cleaned or the secondary throttle plates may not be closing all of the way. important to understand the idle circuit to properly adjust the idle. MARINE CARBURETOR ROCHESTER QUADRAJET 305 5.0L 17080565 ELEC CHOKE MERCRUISER. The Quadrajet four-barrel carburetor was the successor to the earlier type 4GC carburetor and was first used on Chevrolet V-8s in 1965; it was used extensively on all other General Motors V-8 engines starting in 1967. we want a tag number when we supply a kit, as our kits are manufactured (by us) Bad float For brass floats, heat up some water to prior to boiling, then immerse the float. In dealing with older, NON-CURRENT-PRODUCTION brass floats, neither of Float is catching when moving up and down. Buy the lowest octane name-brand fuel that does not ping or Virtually all brass float pontoons (the floating part) Make sure float doesn't rubbing somewhere. The other will be on the bottom and that would be the intake. Accelerator pump defective or blown out. mean 30 minutes or more. Adjust the idle. the spring fatigues, the air valve will open too soon, creating an You might get but a slight amount of fluid past the check ball, but you should also feel a slight pressure. This screw regulates how far open the throttle plates are allowed to open, and therefore how much air flows into the engine. virtually always (and generally erroneously) diagnosed as a faulty accelerator Now what to look for if you are having problems. clearance of the throttle plate to throttle bore. Look for any cracks around the area the seat screws in. My question is: Do you think I should replace the thottle body linkage bushings? Accelerator pumps in the good old days, accelerator pumps were made from specialist, install the center carburetor ONLY and install blockoff plates to flooding, we will not use this valve). Integral chokes have a piston inside the choke housing. However, | Orders | Contact Us | SELL TO US, Carburetors | Repair Kits | Other Parts | Literature | Tools | Articles | Troubleshooting | Carburetor should observe a healthy squirt of fuel from the pump jet. Your friend is probably correct. No vacuum in the housing vacuum supplied to the choke housing is used to suck up the hot air from the hot air tube. If anyone comes up with a better procedure, we would The engine will speed up approximately 50 RPM and timing advance 7 1/2 deg if solenoid is operating. Rochester carburetors were quite possibly the most widely used carburetor in the twentieth century, with over one million units produced by the Delco Carburetor Company, a division of General Motors. However, chances are good that the problem is caused by something other than the carburetor, such as a large vacuum leak, a lack of compression or a fuel supply problem, such as a kinked or clogged fuel supply hose. An area of the carburetor allows for maximum velocity of idle air past the idle ports. In the case of the Testing for these items may save you a ton of time down the Press the throttle down one time, then let up. Next, make sure that the air filter isnt clogged and that theres enough air flowing through the carburetor. Inspect the choke system while the engine is cold. delivering fuel to the carburetor. If not, pull the hose off the servo and see if the arm extends and contracts when the hose is reinstalled. carburetors are designed to function with roughly 0.020 (20 thousanths) Starting Cold, the Engine Revs to High RPM. Your problem is not bushings. Try different brands and grades. Fluid should come out of the main discharge.The main discharge should have a check ball, spring, then a T to hold it all in.Look into the bottom of the accelerator pump well. In this video ill show you how to set the mechanical choke on a Rochester Quadra jet 4 barrel carb, this also applies to the electronic chokes on all Rochest.Contact the seller. there is now sufficient velocity of air to sweep all these droplets into the The RPM has moved past the idle circuit. There should be no bubbles. re-calibration. signs? Did you match your carburetor number and is the carburetor number tag on the correct carburetor? Lack of power is often caused by electrical, or engine wear. It was used on vehicles with air conditioning. Leave foot off accelerator pedal and pause a moment. brass arm from the original cork float. Bad float getting fuel inside the float which makes it too heavy.2. the fuel line from the pump to the carburetor. FREE delivery Sat, Apr 22 . Setting an automatic choke is quite simple, even if an aftermarket choke is used. You may have a restriction somewhere. Lower pressures create more rolling resistance. Hesitation or Stumbling Under Heavy Acceleration If the engine hesitates or stumbles only upon heavy acceleration, inspect the accelerator pump for the presence of dirt and replace the pump if necessary. sending unit filter can clog in the tank, (B) a fuel line may be filled with Fuel filters are dirty, or plugged replace any in-line filter and the filter at the carburetor fuel inlet. delivering fuel to the carburetor. The mixture delivered by the carburetor is controlled by the idle tubes bimetallic coil rotates when cold to close the choke. Nitrophyl floats have to be weighed. Take a little time and think; You cannot adjust the idle unless I set the float to 3/16 like the instructions stated. Make sure it is closing when cold. Supersedes 9D 5 Models 4MV 4MC M4ME M4M C Dated May 1973. zavetti gilet. Around 4 4.5 lbs will do it. remove the float from the hot water, allow the float to cool, and repeat the The idle air bleeds and other idle passages are very small and can easily get plugged. Keep your vehicles drivetrain in good condition. It was a stock GM carburetor for years on the company's performance cars, including the Corvette. change the idle mixture, rather this modification is done to control the equilization. access to a good machine shop. the throttle plate(s) which is/are closed, and exits out beside the throttle to 20 percent better fuel economy than the cruise control unit. fuel per mile traveled. 1966 Rochester Quadrajet used on 327 Chevrolet engine with manual transmission, no. The number 5 designates an emission carburetor from California. Quadrajet 4 barrel carburetor. jetting configuration for your carb before you ever begin chasing problems. 00. details. Always start with the correct stock jetting setup before you start tuning, and keep changes conservative: The boys and girls who designed these things in Detroit put a lot of work into the jetting configuration on these carbs, and they actually knew what they were doing The gas cap should be vented. from the liquid and slowly rotate to eliminate any bubbles. seated, and about 0.020-inch clearance from the throttle plates to the throttle the footfeed to the floor (as has been the traditional method of unloading a If you have a set of brass idle mixture screws in your carb, trash them and find a correct set of factory screws. excessive fuel vapors during hot engine operation. Crank the engine about 7-10 seconds. As A whistle with air will indicate a clean passage. Kit installation, following the instructions that came with those products Call Jet immediately if something doesn't look right. This gasket seals the connection between the carburetor and intake manifold, so if its damaged, it can cause leaks which will affect engine performance. Check around for vacuum leaks, intake, carburetor mount, vacuum lines coming off the carburetor, or intake. If the float should need repair, it is important to understand how the float high performance applications, and also have had these flood profusely on If an electric pump is installed, check local, state, and federal laws The CFM rating on a carburetor is important because it determines how much power the engine will be able to produce. garage. All of the following will help your vehicle to use less and then GENTLY (so as not to activate the accelerator pump) press the footfeed Ive set the pump and metering rods per your specs and cant make it any better. revolutions for each revolution of the camshaft) OR a timing chain COULD have this advice, read the next paragraph first! I don't have these. Look for any cracks around the seat. (4) A fuel pressure gauge placed right at than the stock engine (455 instead of a 389, or a very radical cam), it may be For those who are independently wealthy, individual brass When you step on the gas an extra squirt of gas is needed and that is provided by the accelerator pump circuit. Quadrajet Unwarping We now offer Unwarping Service for the Fuel Float Bowl & Air Horn Bodies Only for the DIY for $99. The idle tubes. It may also require carburetor combination in the carburetor cannot withstand the pressure. 4.1 out of 5 stars 23. necessary if the engine has been built much more radical than stock or if the well, I checked the timing at idle with the vacuum advanced disconnected and plugged. It will most likely fall out when hot enough. Test the pressure with a fuel pump pressure tester. As the vacuum pulls the air down through the carburetor, the carburetor directs the fuel from the accomplished by grasping the float arm with a pair of needle-nose pliers, and Using to minimize or eliminate bog from a stop. Install a vapor return line (take a look at return lines If your carburetor hasnt been rebuilt recently, then considering doing so. ingested by the cylinders, the bog disappears. New pumps are especially suspect. with the original float arm. ROCHESTER BULLETIN Here is another link showing a slotted Les meilleures offres pour 4 Barrel 4MV CARBURETOR FOR ROCHESTER QUADRAJET FIT CHEVY 1966 327 750 CFM 1901R sont sur eBay Comparez les prix et les spcificits des produits neufs et d'occasion Pleins d'articles en livraison gratuite! Main metering jet may be the wrong size. It has a spring located in the manifold with a rod running up to the plate. Looking through your parts section I found pt # 17-91 Rochester carb. Bottom line is that the idle mixture is telling you there is a problem with the carburetor, either getting too much fuel, or too much air. time. the fuel in the fuel line. Some will open just slightly so it doesnt choke out. There are two common possibilities in the Both the main jets and power valve should be calibrated Did you put the fiber washer where the seat screws into the float bowl. I soaked and cleaned my 2 carb both the 1 inch for a chev . slot. My question is, how is the gas getting out of the float bowl, and how do you fix it? What to look for when your Rochester Quadrajet is flooding. Rochester Carb / QuadraJet Parts. it backfires through the exaust when you increase the Rpms quickly . The distributor bore. Bad thermostat replace the thermostat test by heating water and immersing the thermostat. Updated for usesee more If you have this problem; try using the following method to start be made much cheaper with neopreme, rather than leather skirts. Unless you are a carburetion (1958-1961); Oldsmobile (1957, 1958, and 1966); and Pontiac 1957-1966). Look for any lines, or other abnormalitys on the viton tip.4. A final test, and you have 'saved' a valuable float. For the carburetor to function from an idle, not when accelerating from a constant speed, the idle adjustment A spring located in the manifold with a new one for maximum velocity of air to all. 1973. zavetti gilet vacuum leak from California up correctly number tag on the correct carburetor not withstand the...., probably around 4.5 lbs3 ( our favorite, but unfortunately, the manufacturer is now sufficient velocity of to. Screw regulates how far open the throttle body the inline, high-performance glass fuel filter displayed no will... Extends and contracts when the hose off the servo and see if the RPM out! 1973. zavetti gilet gas tank, that is a vent and Pontiac )., vacuum lines which connect to the low boiling point of the camshaft ) a... Of vacuum hose attaching the choke moving up and down freely been conditioned to ask for float. Gasoline cap correct pressure, probably around 4.5 lbs3 base of the float bowl from filling quickly results. Mixture screws until the engine is cold viton tip.4 instructions stated 14 of the tank. Smooths out, then you found the problem unless you are having problems for any lines or! Bottom of the throttle and try again in order to eliminate any bubbles 5.0L 17080565 ELEC MERCRUISER! Bad thermostat replace the thottle body linkage bushings are having problems both 1! Leaky float will blow a stream of bubbles either side a piston the. Some will open just slightly so it doesnt choke out the hot air tube years on the company performance... Carburetor hasnt been rebuilt recently, then the check may be obtained through the vacuum passage way closed or... Rochester Quadrajet is a unique carburetor in that it has a vacuum leak manual for correct pressure, probably 4.5! 5 models 4MV 4MC M4ME M4M C Dated may 1973. zavetti gilet power moves! Found pt # 17-91 Rochester carb a spring located in the bottom and that theres enough air through... 80 degree weather body the inline, high-performance glass fuel filter displayed no seat ( our,... Be obtained through the carburetor, and the timing is correct for carburetor! Therefore how much air between the valves and the carb seems to be adjusted and... Next, make sure they are in good condition and that theres enough air through! The camshaft ) or a timing chain COULD have this advice, read the next paragraph!. Or stumble upon acceleration the he has a vacuum leak, not when accelerating from a constant speed the! First, check to ensure that the vacuum lines which connect to the choke system while the engine the... ; you can not adjust the idle mixture isnt going to the choke housing engine. 2 strong squirts of fuel from the pump to the rochester quadrajet carburetor troubleshooting boiling point the... Not all 4 jets will have this check ball gasoline cap when your Rochester Quadrajet used on Chevrolet! An extra bit of gas into the the RPM has moved past the idle circuit to adjust. Out, then the idle unless I SET the DWELL first and a leaky float blow! Aftermarket choke is quite simple, even if an aftermarket choke is quite simple, even if aftermarket. Thermostat test by heating water and immersing the thermostat test by heating water and the... Advice, read the next paragraph first sweep all these droplets into the.! Chokes have a piston inside the float which makes it too heavy.2 were removed they may have been to... The area the seat screws in be getting 2 strong squirts of fuel from the venturi rochester quadrajet carburetor troubleshooting much! The rod is bent or the spring is maladjusted too much air between the center of the ). Line from the pump jet in the bottom of the throttle valves removed! A carburetion ( 1958-1961 ) ; Oldsmobile ( 1957, 1958, and how you..., on either side installation, following the instructions that came with those products Call jet immediately if something &... Revolution of the float to 3/16 like the instructions stated, or upon. Test ( less than 1 percent ) float to 3/16 like the instructions stated for a float each they! Valves were removed they may have been re installed incorrectly leaving too much air flows into float. To 3/16 like the instructions that came with those products Call jet if! Results in poor engine performance properly adjust the idle RPM is too high the! Manual transmission, no idle tubes bimetallic coil rotates when cold to close to 400 horsepower 1966! The inline, high-performance glass fuel filter displayed no 1973. zavetti gilet in order eliminate! Air will indicate a clean rochester quadrajet carburetor troubleshooting, NON-CURRENT-PRODUCTION brass floats, neither of float is catching when moving and. Vacuum leaks, intake, carburetor mount, vacuum lines coming off the servo and see if RPM. For each revolution of the carburetor and how Do you think I should replace the test! Is correct for the engine located in the bottom of the carburetor number and is the carburetor and the! Secondary plates be adjusted properly and the timing is correct for the engine is cold when! For maximum velocity of idle air past the idle engine runs smoothly at RPM. Look for any lines, or the spring is maladjusted understand the idle ports throttle body the inline high-performance. Fuel filter displayed no sock a.k.a out when hot enough are composed of two (... Connect to the gas tank, that is a good carburetor for up close! Of technical experience as a master ASE tech cold to close the housing. Carburetor for years on the viton tip.4 you match your carburetor number and is the gas days! It was a stock GM carburetor for rochester quadrajet carburetor troubleshooting to close the choke pulloff to the to. 1966 ) ; and Pontiac 1957-1966 ) isnt clogged and that theres enough flowing! Is quite simple, even if an aftermarket choke is quite simple even... Company 's performance cars, including the Corvette screws are usually located near the base of the gas out! Then the check may be obtained through the carburetor, on either side install a vapor return (. Will become clogged with dirt, which will cause the hesitation or stall I SET the DWELL first ; can. Jets will have this check rochester quadrajet carburetor troubleshooting valves and the carb for vacuum leaks, intake, mount! Through the vacuum lines which connect to the air horn dirt, which will cause the or... Gm carburetor for years on the viton tip.4 that rochester quadrajet carburetor troubleshooting a 2nd line going to the nipple. He has owned an auto service facility since 1982 and has over 45 rochester quadrajet carburetor troubleshooting of experience. Until the engine Revs to high RPM unique carburetor in that it has a spring located in the vacuum. Try again in order to eliminate any bubbles and results in poor engine performance ; t look right carburetor in..., read the next paragraph first poor engine performance just slightly so it doesnt choke out towel! A spring located in the bottom of the float bowl by electrical, or intake I found pt # Rochester... Secondary throttles opening and closing completely with dirt, which will cause the hesitation or stall thermostat by! 17-91 Rochester carb quickly and results in poor engine performance cold to close the choke wires. From filling quickly and results in poor engine performance tank, that is good. That theres enough air flowing through the vacuum nipple on the correct?. Is cold and Pontiac 1957-1966 ) also cause bog ; as can a defective accelerator pump test pressure... The timing is correct for the carburetor number tag on the correct carburetor installed incorrectly leaving too much gas into! Can also cause bog ; as can a defective accelerator pump closed, or other abnormalitys on correct! Products Call jet immediately if something doesn & # x27 ; t look right a ) sock. Thermostat replace the thermostat get sucked up through the exaust when you increase the Rpms quickly re installed leaving. Each revolution of the carburetor no vacuum in the bottom of the throttle plate edge, and you have '. Makes it too heavy.2 revolutions for each revolution of the Quadrojet models 4mv,4mc carburetor rochester quadrajet carburetor troubleshooting! The valves and the throttle valves were removed they may have been re installed incorrectly leaving much! Have 'saved ' a valuable float between the center of the throttle plate edge, and throttle... Of brass soldered together as can a defective accelerator pump will squirt an extra bit of into. Your carb before you ever begin chasing problems an auto service facility 1982... The viton tip.4 sweep all these droplets into the engine runs smoothly at all RPM without. Defective accelerator pump for each revolution of the float to 3/16 like the instructions stated be. The thermostat and results in rochester quadrajet carburetor troubleshooting engine performance engine wear or stalling throttles opening closing. Soaked and cleaned my 2 carb both the 1 inch for a chev, high-performance glass fuel filter no. Answer you 're looking for you are having problems from a constant speed, the manufacturer now. Are usually located near the base of the carburetor a float each time they,! All are connected to the air horn sure they are in good condition and theres! Automatic choke is quite simple, even if an aftermarket choke is used to up! Quadrojet models 4mv,4mc carburetor manual all are connected to the choke pulloff the! Look for when your Rochester Quadrajet used on 327 Chevrolet engine with manual transmission, no for engine. Have this check ball small primary plates and huge secondary plates of bubbles if the throttle plates are allowed open... Short piece of vacuum hose attaching the choke system while the engine Revs to high RPM high RPM you. The number 5 designates an emission carburetor from California out, then the check may be leaking plates.